It is known in the art to make a rack with recessed teeth having arcuate roots which mate with a pinion gear having arcuate teeth. To the best of applicant's knowledge, such rack and pinion gear arrangement has never been made with helical teeth. Helical teeth have an advantage that tooth engagement as the gear rotates is modulated over the length of the tooth, obviating the shock of engagement experienced by non-helical teeth. Also, in the prior fabrication of such a rack, the practice has been to: bring a disk cutter, or a set of cutters, into engagement with the work piece; cut a tooth or group of teeth by steadily lowering the cutter against the work piece; separate the cutter and work piece; move the work piece longitudinally; and then cut another groove or tooth. This is a slow process, and precise uniformity of tooth width depends on the skill of the machinist. Also, it could not be used to cut helical rack teeth. While the cutter could be skewed slightly, and the grooves/teeth might appear to be helical, they would in face be merely arcuate teeth skewed with respect to a perpendicular, and would not mate with a helical pinion gear. The present invention teaches a process and tooling for continuously cutting such recessed helical rack teeth.
Cylindrical hobs have been used to cut gear teeth. The gear blank is engaged by the hob and rotated in synchronism therewith. However, this cannot be done to make a rack, because of the straight configuration of the rack work piece.